This project uses a comparative approach to investigate attachment and separation in both infants and parents. Studies in rodents have characterized the ultrasonic isolation call in 1-week-old pups and shown that benodiazepine, adrenergic and opiate receptor ligands have potent effects on this behavior. In studies of parental care, oxytocin was found to induce maternal behavior in anosmic nulliparous, virgin females. Autoradiographic analysis of oxytocin receptors in rat brain revealed a discrete increase in the bed nucleus of the stria terminalis in lactating females. This local induction of oxytocin receptors was reproduced in virgin ovariectomized females by acute administration of estrogen, a treatment that simulates the endocrine milieu just prior to parturition. Studies in pygmy marmosets (Cebuella pygmaea) yielded one of the first quantitative descriptions of a non-human primate in which the male provides most of the parental care. Semi-naturalistic observational studies of this phenomenon were replicated in a controlled, prospective design. During this first year two other studies were begun: one studying the changes in CSF peptides before and after parturition in rhesus monkeys and a second analyzing peptide and steroid content in the milk of various mammals including humans.